Σ Variance validatorv13.22 · is your $OMEGA a valid covariance? (symmetric · PSD · η mean-zero)

Paste a random-effects covariance block. The substrate checks it is a real covariance matrix — symmetric and positive-semidefinite, so every variance ≥ 0 and every correlation ∈ [-1,1] — and that η is mean-zero. A negative variance or a correlation > 1 is witnessed, not guessed.